In situ combustion within a subsurface formation containing petroleum hydrocarbons



United States Patent IN SITU COMBUSTION WITHIN A SUBSURFACE FORMATIONCONTAINING PETROLEUM HY- DROCARBONS Application November 29, 1956 SerialNo. 624,998

4 Claims. (Cl. 16638) No Drawing.

This invention relates to production of petroleum from undergroundpetroleum producing formations. More particularly, this inventionrelates to carrying out an in situ combustion operation within anunderground petroleum producing formation.

Various techniques have been proposed for the recovery of petroleum fromunderground formations and for the treatment of petroleum producingformations. For the recovery of petroleum from petroleum producingformations secondary recovery operations which involve water flooding orthermal recovery methods, in situ combustion, employing at least oneinjection well and at least one production well have been proposed. Insitu combustion has also been proposed as a well remedial treatment toimprove the permeability and/or porosity of petroleum producingformation.

In an in situ combustion operation a high temperature zone isestablished in the petroleum producing formation in the vicinity of thewell bore by suitable heating means. Suitable heating means may comprisean electrical heating device or a gas fired bottom hole igniter orheater.

A suitable device for initiating in situ combustionwithin a bore, holeis described in U. S. 2,722,278. Another technique or method, involvingspontaneous combustion, for initiating in situ combustion is describedin U. S. 2,747,672.

Upon introducing a combustion supporting or an F., usually in the range800-l750 F., created by the reaction between the oxygen and combustibleresidues within the formation, such as combustible residues resultingfrom the distillation and/or thermal cracking of the crude oiloriginally in place or introduced thereinto, will commence to move intothe formation outwardly from the well bore in the direction of flow ofthe hot gaseous combustion products.

Leaving this high temperature zone is a relatively high temperature gasstream at substantially the'same tempera ture which, as it movesoutwardly into the formation, loses heat to the formation. By thismethod the high temperature reaction zone is moved radially outwardlyfrom the well bore without further direct application of heat to thearea immediately surrounding the well bore. The distance the hightemperature reaction Zone moves outwardly, and accordingly the volume ofthe petroleum producing formation swept by or comprised within the hightemperature in situ combustion zone, is determined by the relativemagnitudes of the rate of heat generation (combustion of combustibleresidues) and the rate of heat loss to the surrounding formation.

It has been postulated that the following mechanisms are important in anunderground in situ combustion operation for the movement of the hightemperature zone radially outwardly from the well bore into thepetroleum producing formation. Although the exact mechanism of in situcombustion is not definitely completely known,

2,8 71,941 1C -Patented Feb. 3, 1959 the following sequence of events inan underground in situ combustion operation is postulated and ispresented herein for the purpose of enabling one skilled in the art tobetter understand the practice of this invention and is not to beconstrued as limiting this invention in any way. As the high temperaturereaction zone approaches a given volume of the petroleumhydrocarbon-containing formation the temperature of this volume offormation rises. This results in a reduction in the viscosity of theformation fluids therein due to their temperature increase. These fluidsmay then be moved more readily under the influence of the hot gas streamcontinuously emanating from the high temperature reaction or combustionzone. As the temperature of this volume of formation continues to risedistillations of the liquids therein begin. The products of thesedistillations condense in cooler regions of the formation removed fromthe high temperature combustion zone in the direction of gas flow. Thesedistillations continue as the temperature rises until the heaviercomponents remaining from the petroleum hydrocarbons originally in placewithin the formation or introduced therein prior to effecting in situcombustion begin to crack or otherwise thermally decompose yieldinghydrocarbon gases, coke and similar solid carbonaceous residues. As thetemperature continues to rise and the oxygen content of the incoming gasto the given volume of formation increases due to depletion ofcombustible residues in preceding regions or volumes of the formation, apoint will be reached at which the coke or other combustible residueswill begin to chemically combine with the oxygen with the resultingrelease of heat to the formation and the gas stream emanating therefrom.This heat is carried away by the onmoving gas stream and also to alimited extent by conduction to the adjacent regions of the formation.When the coke or combustible residues have been burned away thereremains a volume of substantially liquid-free formation which, unlessotherwise treated, is then gradually cooled by the relatively coolcombustion supporting gas or air entering the thustreated given portionof the formation via the well bore. From the above-indicatedconsiderations it is obvious that the rate of heat energy releasedwithin the formation should be some function of the quantity of fuel orcombustible residues present therein, which is dependent upon type andquantity of the petroleum originally in place and/ or combustiblematerial or fuel caused to be deposited within the formation in the zoneof in situ combustion. The rate of heat released is also dependent uponthe rate at which oxygen is supplied to the combustion zone or, in otherwords, the rate at which the exothermic combustion process within theformation undergoing treatment is effected. The rate at which heat canbe transferred ahead of the high temperature reaction or combustion zoneshould be dependent on the rate at which the gaseous products ofcombustion leave the high temperature combustion or reaction zone andshould be to some extent dependent upon conduction through the formationitself. Accordingly, some control of the in situ combustion process canbe exercised by controlling the oxidation or combustion processoccurring with the in situ combustion operation, such as by controllingthe amount of oxygen or other oxidizing agent introduced into or presentwithin the high temperature combustion zone in contact with thecombustible residues therein.

Accordingly, it is an object of this invention to provide an improvedmethod for the treatment of petroleum containing or producing formationsto enhance or otherwise improve the recovery of petroleum therefrom byan operation involving in situ combustion.

It is another object of this invention to provide an improved method forcarrying out an in situ combustion operation.

Still another object of this invention is to provide a method foreffecting control of an in situ combustion operation.

Yet another object of this invention is to provide a method forinitiating and/ or maintaining an underground in situ combustionoperation.

How these and other objects of this invention are accomplished willbecome apparent with reference to the accompanying disclosure. In atleast one embodiment of the practice of this invention at least one ofthe foregoing objects will be achieved.

In accordance with the practice of this invention in an in situcombustion operation wherein a subsurface petroleum-containing formationis subjected to a relatively elevated temperature in situ combustion isinitiated and/or maintained therein by introducing into said formationprior to subjecting the same to said elevated temperature an oxidizingagent which reacts with petroleum hydrocarbons in said formation at saidrelatively high temperature to oxidize the same. The oxidizing agentintroduced into the formation to contact the petroleum hydrocarbonstherein, as indicated hereinabove, may per se oxidize or otherwise reactwith the petroleum hydrocarbons in the formation at the relatively hightemperature and/or may thermally decompose, for example, when subjectedto said elevated temperature, or otherwise react with the formationfluids or formation solids present in the formation undergoing treatmentto yield an oxidizing agent or free elemental oxygen which in turnreacts with the petroleum hydrocarbons present in the formation tooxidize the same.

The various materials which may be employed in the practice of thisinvention in an in situ combustion operation to initiate and/or to helpmaintain the same by supplying in part or in full the oxygen (or heat)requirement for 'the in situ combustion process includes such materialsas class A, those materials or compounds which react with the formationfluids, particularly water, to yield elemental oxygen or a thermallyunstable compound which decomposes at the temperature at which in situcombustion is carried out, or at a lower temperature, to yield elementaloxygen; class B, those materials or compounds which directly react withthe petroleum hydrocarbons to oxidize the same under conditions of insitu combustion with the concomitant release of a substantial amount ofheat to increase the formation temperature to an elevated temperaturesufficient for maintaining or initiating in situ combustion; class C,those materials or compounds which react with other materials alreadypresent or previously or subsequently introduced into the formationundergoing treatment to yield eiemental oxygen or an oxidizing agentcapable of oxidizing in situ or otherwise reacting in situ with thepetroleum hydrocarbons contained within the formation; class .D, thosematerials or compounds which react with the formation fluids,particularly water, to yield a thermally unstable oxidizing agent whichdirectly reacts with or oxidizes petroleum hydrocarbons present withinthe formation at said elevated temperature. In some instances thematerials employed in the practice of this invention may possess thecharacteristics of one or more of the above classes. For example, Carosacid (permonosulphuric acid) reacts with water to form hydrogen peroxidewhich decomposes at an elevated temperature to yield elemental oxygen.Caros acid itself reacts directly with hydrocarbons to oxidize the same.Accordingly, Caros acid comes within class A and class B. Caros acidmight also be considered to come within classes C and D. A chlorate,such as an alkali metal .or an alkaline earth metal chlorate, e. g.,sodium chlorate or calcium chlo- N rate, is a material which comeswithin class C, per se, or within class D when acidified with sulphuricacid to yield chloric acid.

.Materials suitable for use in the practice of this in vention forinjection into a subsurface petroleum-containing formation to helpinitiate, promote or maintain in situ combustion therein include suchmaterials as hydrogen peroxide, chromium trioxide, the various alkalineearth metal and alkali metal peroxides, such as barium peroxide andsodium peroxide, Caros acid, perdisulphuric acid, chlorine dioxide, thesulfur oxides, chloric acid, chlorous acid, iodic acid, perchloric acid,periodic acid, the various alkali metal and alkaline earth metalchlorates and perchlorates such as sodium chlorate and sodiumperchlorate, the various alkali metal and alkaline earth metalmanganates and permangantes such as sodium manganate and potassiumpermanganate, the various alkali metal and alkaline earth metalchromates and the peror poly-chromtes such as sodium chromate and sodiumdichromates and their corresponding acids, the various alkali metal andalkaline earth metal nitrates such as sodium nitrate, the variousnitrogen oxides such as nitrogen dioxide, nitrogen tetroxide, ozone, thevarious peracids, organic and inorganic, such as peracetic acid,pernitric or pernitrous acid, fuming nitric acid, fuming sulfuric acid,mercuric oxide, the phosphorus oxides, lead dioxide. Various othermaterials which oxidize petroleum hydrocarbons under temperatureconditions of in situ combustion or which react with formation fluids toform elemental oxygen or hydrogen peroxide or which react with otheradded materials such as strong sulphuric acid or hydrogen peroxide toyield oxidizing agents such as elemental oxygen or hydrogen peroxide areknown and may be employed in the practice of this invention.

The subject invention may be practiced in a single well or a multi-wellin situ combustion operation. In a single well in situ combustionoperation as set forth in copending, coassigned patent applicationSerial No. 576,486, filed April 5, 1956, in the name of Gerhard Herzog,there is described a single well in situ combustion operation as aremedial treatment to increase the productivity and/0r permeability ofan underground petroleum producing or petroleum-containing formation.The practice of this invention is particularly applicable to a wellremedial treatment since by following the practice of this invention theintroduction of oxygen, save perhaps that amount necessary to initiatein situ combustion or in order to reach the desired initial hightemperature required to set off in situ combustion, especially when anelectrical heater or well igniter is employed, via a separate gas streamintroduced through the well bore can be substantially eliminated. Theoxidation reaction or the oxygen required to initiate and maintain thein situ combustion operation in the formation surrounding the well boreis maintained, provided or otherwise generated in situ by introducinginto the formation a material or compound in accordance with thepractice of this invention. The disclosures and teachings of theabove-identified patent application, accordingly, are hereby expresslyincorporated in and made a part of this disclosure.

The practice of this invention is particularly applicable to an in situcombustion operation employing a plurality of wells, that is, at leastone injection well and at least one production well. As in a single wellsystem the total oxygen or heat requirement of the in situ combustionoperation may be supplied by introducing into the formation undergoingtreatment a material or compound in accordance with the practice of thisinvention. Desirably an in situ combustion operation carried out inaccordance with the practice of this invention utilizes extraneouslyintroduced via the well bore elemental oxygen, either substantially pureoxygen, air, or air enriched with respect to oxygen or having a slightlyreduced oxygen content such as an oxygen content in the range 5-15% byvolume.

Exemplary of the practice of this invention a hot, concentrated solutionof an inorganic oxidizing agent or salt, such as sodium nitrate, sodiumchlorate, hydrogen peroxide, sodium chromate-orsodium dichromate, Carosacid and the like, is introduced into the petroleum producing formationin the zone to be subjected to in situ combustion. As the combustionzone approaches the thus-treated portion of the formation containing theoxidizing agent the vaporable liquids, such as water, distills therefromleaving behind a residue of solid and/ or concentrated oxidizing agent.This residual oxidizing agent is subjected to ever increasingtemperatures-until it dc; composes with the liberationof a substantialamount of heat and/or oxidizing agent or elemental oxygen which becomesimmediately available for use in the in situ combustion operation tooxidize the residual petroleum hydrocarbons. Also, the residualoxidizing agent or the oxidizing agent resulting from the hightemperature decomposition may react directly with the petroleumhydrocarbons in the formation. In this manner once a high temperaturezone has been initiated within a subsurface petroleum-containingformation to which had been added a substantial amount of oxidizingagent, e. g., sodium nitrate, not only is the in situ combustionoperation more readily initiated but also in situ combustion is morereadily maintained therein, even in some instances without the need forextraneously introduced elemental oxyg In the event there is employed inthe practice of this invention certain materials such as the alkalimetal peroxides and the alkaline earth metal peroxides which react withwater or acids to yield the corresponding alkali metal or alkaline earthmetal hydroxide or salt and hydrogen peroxide, these materials areintroduced or otherwise deposited within the formation to be treated bydispersing or otherwise carrying the peroxide in a subtantially inertfluid carrier, such as a petroleum fraction. For example, finely dividedbarium peroxide and sodium peroxide is suspended in a liquid oil carrierand injected into the formation to be treated by in situ combustion.Upon introduction into the formation the presence of the formationfluids, that is, the presence of water therein, or the presence thereinof previously or subsequently injected acid, e. g., concentratedsulfuric acid, leads to the reaction with the thus-introduced peroxideto yield hydrogen peroxide which reacts directly with the petroleumhydrocarbons in the formation undergoing treatment or which decomposesto yield elemental oxygen which is employed or otherwise consumed in thesubsequent in situ combustion operation.

Exemplary of the practice of this invention, a hot concentrated aqueoussolution of a metal nitrate, such as sodium or potassium nitrate, or ahot aqueous concentrated solution of a metal nitrate and a metalchlorate, such as sodium nitrate and sodium chlorate, is introduced intoa subsurface petroleum-containing formation in a volume sufficient todisplace the formation water or brine therein for a substantial radialdistance surrounding the well bore, e. g., an amount of solutionsufficient to displace the formation water or brine for a distance of3-25 radial feet from the well bore. Thereafter a bottom hole igniter isintroduced into the well bore and located adjacent the thus-treatedpetroleum-containing formation. That section of the formationimmediately surrounding the well bore is heated to a temperature of atleast about 750 F., preferably in the range 800-1300 F. At the same timewhile the formation surrounding the well bore is being heated a gaseousstream containing elemental oxygen, such as air, is introduced into theformation via the well bore. After a period of time the water in theaqueous solution introduced into the formation surrounding the well boreis evaporated, leaving behind a solid residue of nitrate and/or nitrateand chlorate salts. As the temperature increases these salts decomposewith the evolution of elemental oxygen. The elemental oxygen thusreleased serves to provide in whole or in part all of the oxygenrequirement necessary to effect in situ combustion of the petroleum inthat section of the formabeen established within the treated portion ofthe formation the introdutcion of extraneous oxygen via the well boremay be substantially reduced or terminated, there being sufficientoxygen generated by the thermal decomposition of the nitrate and/ ornitrate and chlorate salts with the formationto effect continued in situcombustion;

For example, once in situ combustion has been adequately established theinjection of air via the well bore into the formation undergoingtreatment may be discontinued and in the place of air there may besubstituted a relatively inert gas or even a gas containing combustiblecomponents therein, such as normally gaseous or vaporized hydrocarbons,e. g., methane, propane, butane and the like, to provide a driving forceand/or part of the heat energy necessary to maintain in situ combustionby thermal decomposition of the nitrates or chlorates and/ or to directthe in situ combustion zone outwardly from the well bore into theformation.

In accordance with yet another embodiment of the practice of thisinvention there is disposed in the sub surface petroleum-containingformation to undergo in situ combustion an oxidation catalyst such as analkali metal hydroxide, e. g., potassium hydroxide, or an alkali metalcarbonate, such as potassium carbonate, or their corresponding lithium,barium or calcium compounds, which exhibit a catalytic effect orotherwise function as oxidation catalysts thereby permitting the in situcombustion to be more readily initiated and maintained within theformation undergoing treatment. This use of an oxidation catalyst to aidor promote an in situ combustion operation is more completely describedand claimed in copending coassigned patent application Serial No.624,995, filed November 29, 1956, in the name of Allen D. Garrison andRobert E. Kunetka.

As will be apparent to those skilled in the art many changes andsubstitutions are possible in the practice of this invention withoutdeparting from the spirit or scope thereof.

We claim:

1. A method of initiating or maintaining in situ com-- troduced to atemperature sufficiently high to effect thermal decomposition of saidcompound therein to yield said oxidizing agent and to cause saidoxidizing agent to oxidize the in place hydrocarbons within saidformation to effect in situ combustion therein.

2. A method of initiating or maintaining in situ combustion within asubsurface formation containing petroleurn hydrocarbons therein whichcomprises introducing into said formation an aqueous solution of anoxygencontaining compound which thermally decomposes to yield elementaloxygen, subjecting that portion of the formation containing thethus-introduced aqueous solution of said oxygen-containing compound to atemperature sufficient to effect thermal decomposition of said compoundtherein to yield elemental oxygen and to cause the thus-produced oxygento effect in situ combustion of said petroleum hydrocarbons therebymaintaining an in situ combustion operation within said formation.

3. A method of maintaining in situ combustion within a subsurfaceformation containing petroleum hydrocarbons therein which comprisesintroducing into said formation an aqueous solution of a nitrate whichunder goes thermal decomposition to yield an oxidizing agent, subjectingsaid formation containing the thus-introduced aqueous nitrate solutionto an elevated temperature and simultaneously introducing into thethus-treated portion aqueous solution of a nitrate is an aqueous sodiumnitrate solution.

References Cited in the file of this patent UNITED STATES PATENTS Ranneyet a1. May 19, 1931 Adams et a1. Aug. 9, 1932 Crawford Nov. 1, 1955 SimmMay 29, I956

1. A METHOD OF INITIATING OR MAINTAINING IN SITU COMBUSTION IN ASUBSURFACE FORMATION CONTAINING IN PLACE HYDROCARBONS WHICH COMPRISESINTRODUCING INTO SAID FORMATION A COMPOUND WHICH UNDERGOES THERMALDECOMPOSITION TO YEILD AN OXIDING AGENT, SUBJECTING THAT PORTION OF THEFORMATION INTO WHICH SAID COMPOUND IS INTRODUCED TO A TEMPERATURESUFFICIENTLY HIGH TO EFFECT THERMAL DECOMPOSITION OF SAID COMPOUNDTHEREIN TO YEILD SAID OXIDIZING AGENT AND TO CAUSE SAID OXIDIZING AGENTTO OXIDIZE THE IN PLACE HYDROCARBONS WITHIN SAID FORMATION TO EFFECT INSITU COMBUSTION THEREIN.